Isotopic constraints on the distribution of chalcophile elements in magmatic systems.

Sulfur is one of the Earth's most important volatile elements and sulphur cycling between the Earth's surface and mantle governs the evolution of the Earth's atmosphere and hydrosphere and the distribution of economically important elements. However, little is known about the sulfur cycle on Earth and the enrichment of S and chalcophile elements in magmas. This enrichment is believed to reflect sulfide saturation (1), which is a consequence of magmatic differentiation and the conversion of the SO42- dissolved in the melt into sulfides (S2-).. If melts become S saturated, the high compatibility of chalcophile elements means they will partition into sulfide liquid, and on cooling, these sulfide liquids will undergo further phase separation and exsolution to form base-metal ore deposits. However, these processes are poorly constrained and it is not clear what the relative roles of magma source heterogeneity, tectonic setting and melt oxidation state on chalcophile element enrichment are.

This PhD will use novel stable isotopes to constrain the roles that mantle source heterogeneity, oxidation state, differentiation and sulfide saturation play in generating magma chalcophile element enrichment. The project will initially focus on well-understood calc-alkaline magma suites where sulfide saturation can be demonstrated and the Skaergaard Intrusion (Greenland), a major layered mafic intrusion with mineralized horizons formed from late-stage sulfide fluids (2). The project will expand to consider magmatic rocks associated with major alkaline-associated hydrothermal mineral deposits and depending on the students' interests, could also incorporate experimental studies of stable isotope fractionation between sulphide and silicate liquids (e.g., 3).

This PhD project is part of a NERC "Security of Supply Minerals" consortium involving 10 UK Universities and a cohort of 6 postdoctoral researchers and 5 PhD students. The student will initially focus on archive calc-alkaline magma suites and Skaergaard samples in order to explore Fe, Zn, Cu and potentially Se stable isotope fractionation during magmatic differentiation processes. This project could also incorporate experimental studies of silicate-sulfide chalcophile element partitioning and stable isotope fractionation, these would be carried out at the University of Edinburgh. The student will then expand the project to consider more complex localities where magmatism is associated with hydrothermal mineral deposits. Target localities for fieldwork and sample collection include Cripple Creek (Colorado), Tuvatu/Vatukoula (Fiji) and Cloncurry (Australia). Finally the student will develop quantitative models of stable isotope fractionation and chalcophile element behaviour during magmatic differentiation with the overall goal of understanding chalcophile element enrichment in magmas.